Linear-to-drum optical scan converter system

ABSTRACT

Optical imaging apparatus for scanning an object supported on a flat platen and projecting the scanned image onto a photosensitive structure in the form of a cylindrical drum. The apparatus is characterized by maintaining constant the conjugate length of the optical path, as well as maintaining the image path perpendicular to the flat platen and the cylindrical drum.

Lahr et a1.

[54] LINEAR-TO-DRUM OPTICAL SCAN CONVERTER SYSTEM [72] Inventors: Roy J. Lahr, Westport, Conn.; James R. Cassano, Penfield, N.Y.

[73] Assignee: Xerox Corporation, Rochester, N.Y.

[22] Filed: Jan. 13, 1970 [21] App]. No.: 2,600

52 use. ..355/8,350/6,355/1l [51] Int. Cl. ..G03g 15/04 [58] Field otSearch ..355/8,7,8l,84, 11,14;

[5 6] References Cited UNITED STATES PATENTS 3,454,335 7/1969 Caldwell et al. ..355/8 3,504,972 4/1970 Suzuki et a1 ..355/84 X 3,062,108 11/1962 Mayo ..355/8 [4 1 Mar. 28, 1972 Primary Examiner-Joseph F. Peters, Jr.

Assistant Examiner-Robert P. Greiner Attorney-James J. Ralabate, Benjamin B. Sklar and John E. Beck [57] ABSTRACT Optical imaging apparatus for scanning an object supported on a flat platen and projecting the scanned image onto a photosensitive structure in the form of a cylindrical drum. The apparatus is characterized by maintaining constant the conjugate length of the optical path, as well as maintaining the I image path perpendicular to the flat platen and the cylindrical um. v

3 Claims, 2 Drawing Figures Lll PATENTEUMAR28 I972 SHEET 1 OF 2 INVENTORS' ROY J. LAHR JAMES R. CASSANO LINEAR-TO-DRUM OPTICAL SCAN CONVERTER SYSTEM BACKGROUND OF THE INVENTION This invention relates, in general, to optical imaging systems and, more particularly, to systems wherein the optical path extends from aflat, document-supporting surface to a cylindrical photosensitive member.

In the process of xerography as described in US. Pat. No. 2,297,291 to Chester F. Carlson, a xerographic surface comprising a layer of photoconductive insulating material affixed to a conductive backing is used to retain electrostatic images. In the customary method of carrying out the process, a

uniform electrostatic charge is placed on the xerographic surface, followed by exposure thereof to a light pattern representing a document or object to be reproduced, thereby dissipating the charge in the areas struck by light. The areas that remain charged form a latent electrostatic image in accordance with the light pattern reflected from the object being reproduced.

The latent electrostatic image is then developed by contacting with finely divided electroscopic marking particles commonly referred to in the art as toner, the marking particles or toner" being attracted to the latent image by the charges retained on the xerographic surface. After development of the electrostatic image the powder image is transferred to another surface by placing the transfer surface in contact with the powder image on the xerographic surface and the two are passed under charging wires which'may be those used to charge the xerographic surface. The transfer surface is thereby charged with negative or positive charges and the oppositely charged powder on the plate is attracted to the transfer surface. The transferred image is then fused to the transfer surface, usually by heat from an incandescent or infra-red source, but in some cases by being exposed to air that is saturated with a solvent for the toner.

It has been found desirable to affix the photoconductive insulator to the periphery of a cylindrical drum so as to facilitate the multistep process involved in forming a copy of the object or input document. Furthermore, it is desirable that the object to be copied be held stationary during the copying thereof to thereby facilitate working with three-dimensional objects or the like and also minimizing document handling. To this end fixed platens on which an object or document is placed have been provided. The optical system is disposed intermediate the platen and the cylindrical drum for convenience in scanning and projection of an image. Furthermore, from the standpoint of compactness of the machine it is desirable to utilize a short conjugate length optical arrangement. In order to produce optimum recordings, in a short conjugate length optical system, the conjugate length of the optical path must be maintained constant and the image path must be maintained at right angles to the platen and cylindrical drum.

Accordingly, it is the general object of this invention to provide new and improved imaging apparatus.

It is a more particular object of this invention to provide a new and improved optical scanning method and apparatus for copying machines utilizing a flat, stationary object-supporting surface and a cylindrical photosensitive recording drum.

Another object of this invention is to provide a new and improved optical scanning device wherein the conjugate length of the optical path between a flat, object-supporting surface and a cylindrical drum is maintained constant.

BRIEF SUMMARY OF THE INVENTION Briefly, the above-cited objects are accomplished by maintaining constant the conjugate length of the optical path between a flat support platen and a cylindrical recording drum and also maintaining a perpendicular orientation between the optical path and the platen and between the optical path and the drum. This is accomplished by the provision of a threecomponent linkage mechanism one component of which moves in a reciprocatory manner parallel to the flat platen and another one of which rotates on the shaft of the recording drum. A lens system or unit is carried by the third component which is pivotally. connected to the other two components by a pair of mirror supporting shafts. The first-mentioned components, therewith support for movement scanning slits, the distance between which is fixed. The distance between each slit and its corresponding surface (i.e., flat platen or cylindrical drum) as will be obvious from the foregoing, is also fixed, consequently, the conjugate length of the optical path is fixed.

To maintain perpendicularity of the mirrors, to their adjacent surfaces, their shafts are connected to cam arms which effect rotation of the mirrors in a predetermined manner such that a plane perpendicular to the mirror always bisects the angle formed between the two of the three components associated with that particular mirror shaft. In this manner the angularity of the mirror remains constant, therefore, if the mirrors are initially set at angles which direct the optical path perpendicular to the flat platen and the drum then the perpendicular relationship will be maintained.

Further objects and advantages of the present invention will become apparent when considered in view of the description of the preferred embodiment of the invention and drawings forming a part thereof.

DESCRIPTION OF THE DRAWINGS FIG. 2 is a perspective view of an optical scanning device representing the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION Referring now to the drawings, especially FIG. 1, reference character 10 designates generally imaging apparatus comprising a cylindrical drum structure 11 having a light responsive surface comprising a photoconductive insulating layer supported by a conductive backing layer. The drum structure 11 is supported for rotation by a shaft 13 which shaft is suitably journaled in the machine frame (not shown).

The xerographic drum need not be in the shape of a right circular cylinder. It could readily be an endless belt with a curved portion thereof passing through an image zone. The shaft 13 is adapted to rotate the drum structure in a counterclockwise direction, in a manner to be discussed hereinafter, such that its surface sequentially passes a series of xerographic processing stations and such that a number of xerographic processing structures can be moved relative thereto. While the light responsive surface is herein described as a xerographic surface, it will be appreciated that it could be any light responsive surface, for example, a photographic film.

The above-mentioned processing stations and structures, for the purposes of the present disclosure, may be described as follows:

A movable charging structure A, which places a uniform electrostatic charge on a portion of the drum. Although other charging devices known to those skilled in the art may be utilized, it is preferable to utilize corona discharge from a wire filament or wire filament array which is maintained at a high potential as described, for example, in US. Pats. No. 2,588,699 to Carlson, No. 2,836,726 to Vyverberg, No. 2,777,957 to Walkup, No. 2,778,946 to Mayo and others.

A moveable imaging structure generally indicated B, through which light patterns of objects to be reproduced pass in order to dissipate the charge in accordance with the light patterns to thereby leave a latent electrostatic image on the photosensitive surface of the drum structure 1 l;

A developing station C, at which developer, including electroscopic marking particles which are charged oppositely to that of the electrostatic latent image, is moved over the drum surface to thereby form a visible image. This may be accomplished with a cascade type of development system which comprises a container or cover with a trough at its bottom containing a supply of developer material comprising a twoelement mixture including the electroscopic marking particles and grossly larger carrier beads. The developer material is picked up from the bottom of the container and dumped or cascaded over the surface of the drum by a number of buckets 5 on an endless driven conveyor.

Optionally, a transfer station D, at which the developed image may be transferred from the drum surface to a record medium;

and a drum cleaning and discharge station E, at which the 1 drum surface is brushed to remove residual marking particles remaining thereon after image transfer.

Illumination emanating from a pair of exposure lamps 14 is reflected from an object (not shown) which is supported on a flat or planar platen 16 thereby forming a light pattern in ac- 1 cordance with the object to be copied. Lamps 14 are supported by a carriage structure 17 which is supported for reciprocating movement by a pair of guide rods 18. Movement of the carriage structure 17 and, therefore, the lamps 14 in the scan direction (i.e. from left to right as viewed in FIG. 1) is accomplished by means of a cable 19 attached to one end of the carriage structure 17 and at its other end to a lamp carriage pulley 21. Rotation of the pulley 21, power to which is supplied through an either-or engage mechanism 22, in a counterclockwise direction, serves to transport the carriage in the scan direction while a carriage return spring 23 serves to transport the carriage to its start-of-scan position.

The light pattern is reflected through a scan slit or aperture 24 which extends transversely of the carriage structure 17 and is disposed in the bottom wall thereof. An object mirror 26, rotatably journaled in a pair of rectangular-shaped links 27 depending from the carriage structure 17, reflects the light pattern through a lens structure generally indicated at 28 and in the direction of an image mirror 29 which is rotatably journaled in pairs of elongated links 31 and 32, the former pair of which rigidly supports the lens structure 28 and the latter pair of which are rotatably supported by the shaft 13 of the drum structure 11. The lens structure 28 preferably constitutes a lens strip optic afir'n'aging device having a short conjugate 1 length. Such a structure or unit 28 may be of a construction 1 well known in the art which produces an upright and reverse reading image. Such a construction may comprise three lens strips each comprising a plurality of lens elements supported such that the lens elements are coaxial thereby forming a plu-i'. rality of imaging devices extending transversely of the ap-j" paratus. Each of the imaging devices is adapted to scan an ele-1 H, "I r mental or discrete area of the portion of the document to be copied which is in the focal plane of the uppermost elements and to project an image of that area upon the drum 11 which is in the focal plane of the lowermost lens elements. It will be appreciated that such a lens structure will have the effect of making a wrong reading image as presented by the mirror 26, right reading, while the mirror 29 will present a wrong reading image to the drum 11. The image mirror 29 reflects the image pattern to the drum surface through an exposure slide of an exposure housing 34. The exposure housing stops unwanted light from striking the drum, while the exposure slide controls the length of time a point on the object of document is exposed to the drum surface. It will be appreciated that since the links 27, 31 and 32 are rigid and connected together, they form a linkage mechanism the distance between the ends of which is constant. Further, since the links 27 are rigidly attached to the lamp carriage structure 17 which moves parallel 6 5 to the platen 16 and the links 32 are fixed radially relative to the surface of the drum, the conjugate length of the optical path from the document to the surface of the drum is constant.

Cam arms 36 and 37 (see FIG. 2) fixed to the shaft ends 38 and 39, respectively, of the mirrors 26 and 29 cooperate with cam structures 41 and 42 to maintain constant angularity between the mirrors and their associated surfaces during a scanning operation. Each of the cam structures 41 (i. e. one adjacent each side of the carriage structure 17) comprises a pair of arms 43 and 44 the latter of which is provided with a protuberance 46 which engages the cam follower 36. The arms 43 and 44 are pivotally connected to links 27 and 31 as well as to each other to enable changing of the relative position thereof which effects relative rotation of the object mirror 26 through interaction of the cam follower 36 and the protuberance 46. A bias member in the form of a coil spring 47 insures proper engagement of the cam follower with the protuberance. Similarly, each of the cam structures 42 (i. e. one adjacent each side of the carriage structure 17 comprises a pair of arms 48 and 49, the latter of which is provided with a protuberance 51 which engages the cam follower 37. The arms 48 and 49 are pivotally connected to links 31 and 32 as well as to each other to enable changing of the relative position thereof which effects rotation of the image mirrors through interaction of the cam follower 37 and the protuberance 51. A bias member in the form of coil spring 52 maintains proper engagement of the cam follower and protuberance 51. It can be seen that the relative rotation referred to above is with respect to the pairs of links 27 and 31 and 32 which has the effect of maintaining a constant angularity of the mirrors 26 and 29 relative to their associated surfaces.

It will be apparent that as the lamp carriage moves through a scan cycle, the links 32 supporting the exposure slit 33 move in a clockwise direction relative to the drum structure 11. As this movement takes place, a charging unit in the form of a corotron 53 places a uniform electrostatic charge on the xerographic surface carried by the drum structure. The corotron unit 53 is rigidly attached to the exposure housing 34. Dissipation of the aforementioned charge in accordance with light patterns representing a document to be copied is accomplished by virtue of such clockwise movement of the exposure housing 34.

As mentioned previously, the return spring 23 serves to move the lamp carriage and links back to their original position. At such time power is transmitted via the unit 22 to drum pulley 54, through belt 56 and an output pulley 57, the pulley 54 being attached to an extension 58 of the drum shaft through an overrunning clutch 59 of conventional design. Thus, the latent electrostatic image on the drum surface is driven or rotated past the xerographic stations. The clutch 59 constitutes a drawn cup roller clutch and bearing assembly which is commercially available, being manufactured by the Torrington Co., Torrington, Connecticut. The construction of the clutch is such as to allow relative rotation between it and the drum shaft in only one direction while causing rotation of the drum therewith in the opposite direction.

It will be appreciated that due to the geometry of the structure hereinabove described and because of the conversion of linear displacement to rotational displacement, displacement of the exposure slit is less than that of the scan slit 24, accordingly, a compensating mechanism generally indicated by reference character 61, is provided. The mechanism 61 comprises a cam member 62 adapted to move angularly with the links 32 and a cam follower 63. Movement of the cam 62 clockwise causes a counterclockwise rotation of the cam follower 63 which, in turn, effects counterclockwise rotation of the pulley 59 through belt 64 thereby effecting counterclockwise rotation of the drum simultaneously with the clockwise rotation of the exposure slit 33. The profile of the cam 62 is such as to move the surface of the drum precisely equal to the differential between the scan and exposure slits.

It will be appreciated from the foregoing that during scanning or while the latent electrostatic image is being placed upon the drum, the drum is rotated counterclockwise at a constant speed relative to the optical path while the exposure housing is rotated clockwise; but during development, transfer and cleaning only the drum rotates which rotation is in the counterclockwise direction.

While the present invention has been described with reference to the structure disclosed herein, it is not intended that it be limited to the specific details and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or scope of the claims forming a part hereof. For example, the cam arins 36 and 37 and the protuberances 46 and 51 which serve to maintain the angularity of the mirrors such that the optical path is always perpendicular to the platen and the rotating drum, could be replaced by a pair of tubular telescoping members to which the arms 43, 44 51 and 52 would be pivotably attached. with such an arrangement the bias rings 47 and 52 would not be necessary. Furthermore, constant speed rotation of the drum could be accomplished either by mounting the stator of the motor which rotates the drum, on the arm 32, or a speed reducing system such as a planetary ball-bearing is employed, the reducer case may be secured to the arm 32. Thus, whether I a point is scanning along the platen or is stationary, the drum surface passes the exposure slit at a uniform speed relative to the optical path. This arrangement would be quite useful, for instance, if single sheet documents were to be mechanically tractored past a fixed point of the platen as in a dual mode input copier (sheet feed or book copying option).

What is claimed 1. Imaging apparatus comprising: a flat document supporting surface; an arcuate photosensitive recording surface; scanning structure supported for reciprocating movement parallel to said document supporting surface; an exposure structure supported for rotation about said arcuate recording surface at a fixed distance therefrom; lens structure and means for supporting said lens structure intermediate said scanning structure and said exposure structure at a fixed distance from each; an object mirror and means for rotatably supporting said object mirror intermediate sait i scanning and len sstructures.for reflecting light rays emitted from the scanning structure, said light rays being reflected in the direction of said lens structure; .an image mirror and means for rotatably supporting said image mirror inten'nediate said exposure and lens structures for reflecting light rays from said lens structure, said light rays being reflected in the direction of said exposure structure; means for rotating said mirror simultaneously with movement of said scanning structure to thereby maintain the angular positions of said object mirror relative to said document supporting surface and said image mirror relative to said arcuate surface substantially constant; and

said lens structure serving to focus light rays on said image mirror, said light rays being reflected by said object mirror to said lens structure.

2. Apparatus according to claim 1 wherein said means for supporting said mirrors comprises pairs of relatively rotating links, each pair of links forming substantially an acute angle therebetween, and

wherein said means for rotating said mirrors comprises cam followers connected to said means for supporting said mirrors and cam means and means for moving said cam means simultaneously with rotation of said links, said movement of said cam means being along the bisector of the acute angles between said pairs of links.

3. Apparatus according to claim 2 wherein said means for moving said cam means comprises pairs of rotating arms connected to said pairs of links so as to be rotated thereby and form therewith parallelograms.

i k i 

1. Imaging apparatus comprising: a flat document supporting surface; an arcuate photosensitive recording surface; scanning structure supported for reciprocating movement parallel to said document supporting surface; an exposure structure supported for rotation about said arcuate recording surface at a fixed distance therefrom; lens structure and means for supporting said lens structure intermediate said scanning structure and said exposure structure at a fixed distance from each; an object mirror and means for rotatably supporting said object mirror intermediate said scanning and lens structures for reflecting light rays emitted from the scanning structure, said light rays being reflected in the direction of said lens structure; an image mirror and means for rotatably supporting said image mirror intermediate said exposure and lens structures for reflecting light rays from said lens structure, said light rays being reflected in the direction of said exposure structure; means for rotating said mirror simultaneously with movement of said scanning structure to thereby maintain the angular positions of saiD object mirror relative to said document supporting surface and said image mirror relative to said arcuate surface substantially constant; and said lens structure serving to focus light rays on said image mirror, said light rays being reflected by said object mirror to said lens structure.
 2. Apparatus according to claim 1 wherein said means for supporting said mirrors comprises pairs of relatively rotating links, each pair of links forming substantially an acute angle therebetween, and wherein said means for rotating said mirrors comprises cam followers connected to said means for supporting said mirrors and cam means and means for moving said cam means simultaneously with rotation of said links, said movement of said cam means being along the bisector of the acute angles between said pairs of links.
 3. Apparatus according to claim 2 wherein said means for moving said cam means comprises pairs of rotating arms connected to said pairs of links so as to be rotated thereby and form therewith parallelograms. 